Help on defeating Omega Weapon?

[John Smith]

Title

The characters I use are: Squall, Rinoa and Selphie.

I've been trying to use Rinoa's Comine Limit Break so that I can use Invincible Moon, but it just doesn't seem to come. If this succeeds or not, I make Squall use Aura on Selphie, so that she can last a little longer to find "The End" in her Roulette Limit Break. I've read this technique in a walkthrough, although in vain. I've ran into The End a couple of times, but I hit the button so fast that it passes right in from of my eyes >.<

Oh, by the way, I hope I'm not confusing Omega Weapon with Ultima Weapon =P